The anterior cruciate ligament (“ACL”) is one of the major ligaments in the knee that connects the thigh bone (“femur”) to the shin bone (“tibia”). The ACL is critical to the stability of knee during daily and sports activities. The ACL consists of two functional bundles named for the place where they attach on tibia. Specifically, the two bundles are the anteromedial (“AM”) bundle, which inserts more anterior (towards the front) and medial (towards the inside) of tibia, and the posterolateral (“PL”) bundle, which inserts most posterior (towards the back) and lateral (towards the outside) of tibia. The AM bundle is the primary restraint to anterior tibial translation throughout the knee flexion. The PL bundle also contributes to the anterior tibial stability at low flexion angles and primarily provides rotational stability to the joint. Although the two bundles have slightly different functions, the bundles do not work independently, but work together to keep the knee stable while still allowing jumping, running, and the like.
There is a high prevalence of ACL injuries both in athletic and non-athletic population. ACL reconstruction is commonly performed to replace an injured ACL. The goal of ACL reconstruction is to restore the native anatomy and function of the ACL. However, osteoarthritis has been reported among patients who had an ACL reconstruction surgery. Improving ACL reconstruction techniques that may restore normal knee stability and prevent joint degeneration remains a subject of continuing debate in sports medicine research.
Currently there are three types of methods and corresponding implants that have been used in ACL reconstruction surgery. The three types are the single-bundle reconstruction, the double-tunnel, double-bundle reconstruction, and the single-tunnel, double-bundle reconstruction.
In a single-bundle reconstruction, the ACL is restored using one graft bundle. Two tunnels (one on tibia and one on femur) are drilled through the knee to house the one graft bundle. One tunnel can be drilled in the center of the attachment of the old ACL on the tibia, right between the AM and PL bundle. The other tunnel can be drilled in the center of the attachment of the old ACL on the femur. Since single-bundle constructions emphasize only on one bundle, typically the AM bundle, it can not recreate the two functional bundles of ACL. Studies have shown that single-bundle ACL reconstruction fails to restore tibial rotation to the intact level. Patients continue to report a feeling of rotational instability and have developed degenerative changes in the knee joint. These observations are attributed to the limitation of using single-bundle ACL reconstruction to reproduce both functional bundles of ACL.
In order to improve on single-bundle ACL reconstruction, especially to provide a better rotational stability, double-tunnel, double-bundle ACL reconstruction was introduced, where ACL is restored using two graft bundles. Compared to single-bundle reconstruction, there are some benefits of a double-bundle reconstruction. Since double-tunnel, double-bundle reconstruction restores both of the AM and PL bundles, it can better restore knee stability compared to single-bundle reconstruction. Nevertheless, double-tunnel, double-bundle reconstruction is a technically challenging procedure. For example, instead of drilling two tunnels for one graft bundle, as in single-bundle reconstruction, double-tunnel, double-bundle reconstruction requires that four tunnels be drilled. The four tunnels include two tibial and two femoral tunnels, for housing two bundles. By drilling two more tunnels, there is an elevated risk of damage to the bone bridge between the two tunnels and an excessive loss of bone. Furthermore, double-tunnel, double-bundle reconstruction is also associated with an increase in the duration of surgery and higher cost compared to the single bundle reconstruction. These limitations in the current designs of the ACL reconstruction techniques leave a large scope for an improvement in the surgery.
To address the deficiency in double-tunnel, double-bundle ACL reconstruction, single-tunnel, double-bundle ACL reconstruction was introduced. Single-tunnel, double-bundle reconstruction uses a single femoral and tibial tunnel and an implant that separates the graft into AM and PL bundles. This reconstruction not only allows the reconstruction of the two functional bundles of the ACL in a single tibial and femoral tunnel to provide superior stability than single-bundle ACL reconstruction, but also is technically less demanding, and decreases operative time. Currently there are two types of implants designed for single-tunnel, double-bundle ACL reconstruction. These implants include the AperFix and Femoral INTRAFIX implants. AperFix is a registered trademark of Cayenne Medical, Inc. of Scottsdale Ariz. INTRAFIX is a registered trademark of Johnson & Johnson of New Brunswick, N.J. There is evidence that neither of these implants can restore normal knee biomechanics.
Therefore, it would be desirable to have an improved system and method for ligament reconstruction, which can better restore the native anatomy and function of the ligament or ligaments in a joint.